Relationship of Vitamin D Deficiency with Cervical Vertebral Maturation and Dental Age in Adolescents: A Cross-Sectional Study

Background Considering the high prevalence of vitamin D deficiency and its effect on growth and development, the assessment of the dental age and skeletal age with regard to vitamin D deficiency status could influence the treatment planning of growth modification treatment. This study aimed to assess the relationship between vitamin D deficiency, cervical vertebral maturation (CVM) as an indicator of skeletal age, and dental age in adolescent patients. Methods In this cross-sectional study, the chronological age of 52 orthodontic patients aged between 10 and 14 years was recorded, and their serum level of vitamin D was determined using a radioimmunoassay test. The patients were then divided into three groups based on their serum vitamin D level: severe deficiency, moderate deficiency, and the control group with normal vitamin D. The panoramic radiographs of patients were assessed to determine their dental age using Demirjian's method. CVM was determined on lateral cephalograms using Baccetti's classification to specify the skeletal age. Data were analyzed using a t-test, linear regression, ordinal logistic regression, and Pearson's correlation coefficient (at P < 0.05, confidence interval = 95%). Results Skeletal age showed a significant difference between the group with severe vitamin D deficiency and the control group (P=0.01); however, such difference was not observed between the group with moderate vitamin D deficiency and the control group (P=0.12). Dental age was not significantly different between the groups with vitamin D deficiency and the control group (P=0.26 for severe, and P=0.39 for moderate deficiency). Conclusions A less advanced skeletal maturation was observed in adolescents with severe vitamin D deficiency; however, dental development was not affected by this deficiency. Vitamin D status is better to be considered in decision-making for the initiation of growth modification orthodontic treatments.


Introduction
Vitamin D plays a fundamental role in bone development and muscle function. It eliminates calcium and phosphate from the kidneys, suppresses the parathormone, and induces the osteoblasts to form new bone. Vitamin D defciency causes osteomalacia in children, results in recurrence and aggravation of osteopenia and osteoporosis, and can lead to bone fracture in adults. It can also cause growth retardation, muscle weakness, skeletal deformities, and hypocalcemia [1]. Te role of vitamin D defciency in the etiology of other disorders such as diabetes mellitus, multiple sclerosis, and auto-immune problems has also been established [2].
Vitamin D defciency has a high prevalence in children and adults. Evidence shows that in the past two decades, vitamin D defciency has become increasingly prevalent in China, Turkey, India, Iran, and Saudi Arabia with a prevalence rate ranging from 30% to 93% [3,4]. Te prevalence of vitamin D defciency is higher in countries with insufcient exposure to sunlight, insufcient dietary intake of vitamin D, and air pollution [5]. Vitamin D defciency is now a pandemic, and the main reason is believed to be insufcient exposure to sunlight [1].
Data obtained from the growth charts of children can help dental clinicians and orthodontists fnd the best time for the initiation of growth modifcation treatments [6]. It also helps in estimating children's growth and development status to prevent oral and dental disorders [7]. Many physical parameters such as height, weight, skeletal maturity, and dental development can be used to determine the growth and development stage [8]. Dental age is determined based on the order of tooth eruption, while skeletal age is determined by assessing the maturation of the C2 to C4 cervical vertebra. Cervical Vertebral Maturation (CVM) is commonly used to determine skeletal age [9].
A delay in dental age and skeletal age, when compared to the chronological age, has been observed in patients with a growth hormone defciency, HIV-positive patients, those with Celiac disease, and underweight patients [10][11][12][13]. On the other hand, accelerated dental and skeletal age has been reported in obese children [14,15]. Patients with vitamin D defciency may also experience retardation in their growth and development [16].
Considering the high prevalence of vitamin D defciency, its efect on growth and development, and the importance of determining patients' growth status in the treatment planning of growth modifcation treatments, the need for assessment of the dental age and skeletal age with regard to vitamin D defciency status is highlighted. Tis study aimed to assess the association of vitamin D defciency with dental and skeletal age in 10 to 14-year-old adolescents, using panoramic radiographs and lateral cephalograms.

Methods
Tis cross-sectional study evaluated 52 orthodontic patients aged between 10 and 14 years presenting to the Orthodontic Department at Shahid Beheshti School of Dentistry, Tehran, Iran, following the appropriate institutional ethics approval (IR.SBMU.RIDS.REC.1394.11). Te study design was in accordance with the Helsinki Declaration of Human Rights. All the patients had panoramic radiographs and lateral cephalograms obtained for their orthodontic treatment, therefore eliminating the need for unnecessary radiation exposure during the research. All the patients and their parents were informed about the study and the parents signed the informed consent forms.
Te sample size was calculated to be 51 (N � 17 in each group) using Power and Sample Size Calculation software version 3.0.43. Te inclusion criteria consisted of an age between 10 and 14 years, having panoramic radiographs and lateral cephalograms taken for orthodontic treatment, willingness to participate in the study, and presence of signed informed consent forms by the parents.
Te exclusion criteria were sunbathing more than once a week, taking vitamin D supplements, consumption of vitamin D-rich foods and drinks more often than once a day since the initiation of orthodontic treatment, a history of systemic diseases, medication intake, craniofacial syndromes, the bilateral missing of mandibular teeth, poor quality of radiographs, and not performing blood test in the designated laboratory. It should be mentioned that the exclusion criteria were evaluated according to the parent's responses to the questions.
After obtaining the parents' consent, all patients underwent blood tests in the designated laboratory to determine their serum 25-hydroxy vitamin D level, using chemiluminescence immunoassays (CLIA). All blood tests were performed during the fall season to eliminate the efect of seasonal changes in vitamin D levels. Te patients and their parents were informed of the test results and were educated about the role of vitamin D in the body. Te test results were provided to the parents, and they were referred for medical consultation if needed. Te patients were classifed into three groups according to their 25-hydroxy vi- Tuusula, Finland) was performed according to Baccetti's modifed protocol [17]. Te radiographs were converted to JPEG (Joint Photographic Experts Group) fle format using Digora ® software version 8.2 (Strasbourg, France) and observed using Photoshop software (Adobe ® , San Jose, CA, USA). Magnifcation of ×150 was used for more accurate observation when required. In order to prevent errors in the determination of skeletal age, the evaluation of all lateral cephalograms was confned to the cervical vertebrae by the observer to determine the skeletal age without observing the teeth. Two calibrated, trained orthodontists, blinded to the chronological age and serum vitamin D level of patients, independently determined the CVM stage and the skeletal age. In cases of disagreement, a third blind observer (orthodontist) also reviewed the radiographs. For each patient, two variables, including the presence/absence of concavity in the inferior border of CV2, CV3, and CV4; and the body shape of CV3 and CV4 (trapezoidal, horizontal rectangular, square, and vertical rectangular) were evaluated, as presented by Baccetti [17]. According to these two variables, the patients were assigned to one of the skeletal maturation stages (CVM1 to CVM6) as presented in Figure 1.
Te panoramic radiographs (Soredex ® Cranex-D, Tuusula, Finland) were also independently evaluated by two calibrated orthodontists, blinded to the chronological age and serum vitamin D level of patients, to determine the dental age according to Demirjian's method [18]. For this purpose, the calcifcation stage of seven permanent teeth in the mandibular left quadrant (from tooth number 24 to 18) was scored individually from A to H. Te standard scores of teeth were separately reported for males and females. A total score of dental maturation, which was the sum of individual scores, was reported for each individual. Tis total score was converted to dental age (in years) according to a standard table. Te scores given to diferent calcifcation stages of teeth were determined according to Demirjian and Goldstein, as presented in Figure 2 [18].
Data were analyzed using SPSS (Statistical Package for the Social Sciences) software version 21.0 (SPSS ® Inc., IL, USA).
After the primary assessment of all radiographs, 10 radiographs were randomly selected and re-evaluated after two weeks to assess the intraobserver error. Te kappa coefcient was also calculated to assess the interobserver agreement. Te mean kappa coefcient for the intraobserver agreement was also calculated for dental age and skeletal age determination.
Te mean dental age of patients was compared among the groups using a t-test. Te linear regression model was applied to compare dental age among the three groups after controlling for chronological age and gender. Since the CVM stage was a descriptive variable, an ordinal logistic regression model was used to compare the skeletal age among the groups after controlling the chronological age and gender. Pearson's correlation test was used to assess the correlation between dental age and chronological age in each group. P < 0.05 was considered statistically signifcant. Te body of C3 and C4 is horizontally rectangular. Maximum mandibular growth has occurred one to two years prior to this stage. CVM 5: concavity still exists in the inferior border of C2, C3, and C4. Te body of at least one of the C3 and C4 is square-shaped. If not, it is horizontally rectangular. Maximum mandibular growth has ended at least one year prior to this stage. CVM 6: concavity still exists in the inferior border of C2, C3, and C4. Te body of at least one of the C3 and C4 is vertically rectangular. If not, it is square-shaped. Maximum mandibular growth has ended at least two years prior to this stage.
International Journal of Dentistry 3

Results
A total number of 52 participants were included in the present study. Te intraclass correlation coefcient was found to be excellent for both the calcifcation stage of teeth (0.99) and the CVM stage (0.95). Te mean kappa coefcient for the intraobserver agreement was 95% for the determination of skeletal age and 99.9% for the determination of dental age. Te mean kappa coefcient calculated to assess the interobserver agreement was found to be 92.6% for the determination of CVM stage, and 99.9% for the determination of dental age, which indicated excellent agreement between the two observers. Tis value was 100% for the determination of maturation stages for the central incisor and frst molar teeth. Evaluation of gender distribution among the three groups revealed no signifcant diference in the distribution of males and females (P � 0.94). Similarly, the distribution of chronological age between the groups was not signifcantly diferent (P � 0.29).
After controlling for chronological age and level of vitamin D, the results showed that dental age and skeletal age were not signifcantly diferent between males and females (P > 0.05).
According to the results of Pearson's correlation coefcient, a positive correlation was detected between dental age and chronological age in all patients (r � 0.6, P value <0.001). A positive correlation between dental age and skeletal age was also established (r � 0.7, P value <0.001, according to Spearman's rank correlation). Table 1 presents the distribution of CVM stages among the three groups based on vitamin D levels. Te highest frequency of CVM 1, CVM 2, and CVM 3 was noted in the severe vitamin D defciency group, while the highest frequency of CVM 4 and CVM 5 was noted in the control group with sufcient serum levels of vitamin D. Since all patients were between 10 and 14 years old, none of them was in CVM stage 6. Table 2 shows the mean ± SD of dental age among the three groups based on vitamin D levels. As presented in Table 3, after controlling for chronological age and gender, the results revealed that dental age was not signifcantly diferent among the three groups (P > 0.05). However, a comparison of skeletal age among the three groups revealed a signifcant diference between the group with severe vitamin D defciency and the control group (P � 0.01). Te same signifcant difference was not observed between moderate vitamin D defciency and control (P � 0.12).

Discussion
Te developmental stage of adolescent orthodontic patients has a signifcant role in treatment timing and can be determined using diferent indicators. Presently, the dental age and skeletal development stage are used as the main indices of skeletal growth and maturation in dental practice [19]. Tese two variables are more valuable in clinical assessments than chronological age and gender-related characteristics [11]. Vitamin D plays a fundamental role in the development, metabolism, and function of hard tissues; therefore, its defciency contributes to growth retardation [1].
Tis study assessed the association of vitamin D defciency with skeletal age and dental age in adolescents compared to a normal control group. Te results indicated that, although there was no signifcant diference in dental age between the group with vitamin D defciency and the control group, the skeletal growth delay might be attributed to severe vitamin D defciency [20]. Tis fnding could help dentists to better arrange orthodontic treatment plans according to the patient's skeletal age while considering their serum level of vitamin D. Te absence of correlation between vitamin D level and dental development in adolescents could be attributed to the timing of major dental development, happening earlier in life.
In the present study, skeletal age was determined based on lateral cephalogram using the method described by Baccetti et al. [17]. Evidence shows a highly signifcant correlation between this method and the skeletal age determined based on hand-wrist radiography using Bjork's method in both males and females. Terefore, the determination of the CVM stage on lateral cephalograms is the most favorable method for the assessment of skeletal age in orthodontic patients, since it is faster and has a lower patient radiation dose [21,22].
Several techniques are available to estimate and determine dental age; Demirjian and Goldstein method [18] is one of the most used methods for the assessment of dental age [23]. However, the selection of dental age assessment methods depends on the study population [18,24,25]. In the present study, considering the accuracy, applicability, and reproducibility of Demirjian's method for assessment of dental age in both males and females, this method was employed [26,27].
In the present study, a positive correlation between dental age and chronological age and also a positive correlation between dental age and skeletal age was established in all patients irrespective of their vitamin D level. Cisternas et al. in their study on 657 panoramic radiographs and lateral cephalograms of 5 to 15-year-olds found a signifcant correlation between dental and skeletal maturation, which is in line with the results of the present study [28]. Similarly, Howell in his study on 90 panoramic radiographs and lateral cephalograms, showed a signifcant correlation between dental age determined by Demirjian's method and skeletal maturation determined by Baccetti's method. He recommended the assessment of panoramic radiographs for the calculation of dental age using Demirjian's method as a tool for the estimation of skeletal maturation state, which could be helpful in orthodontic treatment planning for British patients [29].
Te efect of vitamin D on dental maturation has been evaluated in a study by Backstrom et al., indicating that vitamin D supplementation in immature infants did not signifcantly enhance dental maturation. However, the consumption of vitamin D supplements by pregnant mothers would improve dental maturation in their infants [30]. Although the present study was performed on adolescents, dental maturation was not observed to be afected by serum vitamin D levels.  International Journal of Dentistry Measurement of the serum level of 25-hydroxy vitamin D is the best indicator of vitamin D sufciency in an individual [31]. However, it should be noted that the serum level of vitamin D is afected by seasonal changes, with the highest and lowest levels in summer and fall, respectively. Terefore, in the present study serum vitamin D level of all patients was measured in the fall season [1,32]. Chronological age can also afect the serum level of vitamin D [33]. Terefore, studies on serum levels of vitamin D should assess patients in a specifc age group. In this study, patients aged between 10 and 14 years were evaluated since most interceptive orthodontic and pediatric dentistry procedures are performed in this age range. Furthermore, the determination of CVM stage and dental age on radiographs has the highest accuracy in this age range [34]. After the age of 14, most teeth have already developed, hence, the accuracy of radiographic assessment would decrease [25,35].
Considering the association between severe vitamin D defciency and less advanced skeletal maturation in adolescents aged between 10 and 14 years in the present study, it is important to monitor the serum level of vitamin D in this age group.
One limitation of the present study was associated with convincing the participants for performing blood tests in the designated laboratory and the fuctuations in vitamin D levels depending on the season and for individuals over time. Furthermore, some radiographs in patients' electronic fles did not fulfll image quality requirements for the determination of dental or skeletal age. Another limitation was attributed to the fact that some children had received vitamin D supplements as part of their school programs.
Further studies with a larger sample size are required for more defnitive conclusions. In addition, longitudinal studies are suggested following the administration of vitamin D supplementation for children with vitamin D defciency to better evaluate the correlation.

Conclusions
Within the limitations of the present study, it can be concluded that vitamin D status is better to be considered in decision-making for the initiation of growth modifcation orthodontic treatments.

Data Availability
Te datasets used and/or analyzed during the current study are available from the corresponding author upon reasonable request.

Conflicts of Interest
Te authors declare that they have no conficts of interest regarding the publication of this article.